My ex My baby

So me and this guy we will call him jake had been talking for a while and we both agreed that we would be friends untill he gets settled into his 2 new jobs and college because i realize it is a lot to have on your plate. So right now me and him are just friends, but the day after me and jake broke things off i got a text from my ex. It started off as a normal conversation because when we broke up we both said that we would be there for each other no matter our status. So i figured he just needed someone to talk to, and as the conversation went on i said that we should hang out to catch up and talk in person about the subject. Keep in mind that during all of this he was posting about his "girlfriend". then he begun to say that i was the only one that he would trust losing his virginity to. So i told him that he has a girl and shit. He told me that they werent together but just a thing. So i said how do you think she would feel if she found out that the guy she is talking to and tryinv to be in a relationship with went to his ex to fuck her. Sorry for my language but he said after that how would she know unless you say something. But i domt want tp help him cheat on his girl because i wouldn't want a guy to cheat on me i know how that feels but he thinks that when he gets back to colorado we are going to hang out and have sex. I don't want that to happenen and dont know what to tell him or his girl or if i should at all